As background, as used herein, the term "pasty products" is defined as a product capable of forming an adherent mass, but whose consistency nevertheless allows it to be pumped. In other words, a pasty product exhibits coherent mass flow when a pressure is applied to it, either mechanically (such as, the action of a plunger) or pneumatically (such as, by pressurizing of a vessel).
When filling containers with a pasty product, it is extremely desirable to develop a system wherein the container is filled cleanly with the pasty product and the pasty product is precisely metered into the container.
First, it is desirable to fill the container cleanly without soiling its edges. Maximum cleanliness along the closure zones of the container, in turn, maximizes the leakproofness of the container, particularly in the case where this closure is effected by heat sealing.
This requirement leads to particular difficulties if the pasty product is of fibrous texture, which further increases the volume of product capable of adhering to the metering head. In this situation the fibres hanging from the metering head are capable of soiling the closure zones of the container as it arrives and departs.
Second, the greatest possible metering precision is desirable in order to ensure as complete a filling as possible of the container with the minimum residual volume or space from the closure head.
In order to ensure a precise metering, the prior volumetric metering devices typically end of a metering plunger sliding in a cylinder connected, on the one hand, to a supply conduit communicating with a pressurized chamber containing the pasty product and, on the other hand, to a delivery conduit permitting delivery of the metered product towards the container.
Systems of valves placed on the supply conduit and on the delivery conduit ensure correct order of the pumping phases (filling/delivery) in synchrony with the movement of the plunger.
In order to achieve clean filling, in prior metering devices for pasty products, a cutting system, for example a guillotine, is provided at the outlet of the delivery conduit. Such a cutting system permits the metered portion to be separated from the dead volume of product remaining in the delivery conduit and in the metering cylinder.
In addition to its mechanical complexity (valves to synchronize with the movement of the plunger, guillotine system, etc), the prior system has the disadvantage of always leaving a dead volume where the product is capable of accumulating. For this reason, this dead volume risks damaging the biological quality of the product being metered because of the possible development of germs therein.